Base resistant specialty fluoroelastomers made from copolymers of ethylene (E), a perfluoro(alkyl vinyl ether) (PAVE), tetrafluoroethylene (TFE) and a cure site monomer are known in the art (U.S. Pat. No. 4,694,045). In addition to being resistant to attack by strong bases, these fluoroelastomers have good sealing properties at both low and high temperatures and exhibit low swell in oil.
In order to fully develop physical properties such as tensile strength, elongation, and compression set, elastomers must be cured, i.e. crosslinked. In the case of fluoroelastomers, this is generally accomplished by mixing uncured polymer (i.e. fluoroelastomer gum) with a polyfunctional curing agent and heating the resultant mixture, thereby promoting chemical reaction of the curing agent with active sites along the polymer backbone or side chains. Interchain linkages produced as a result of these chemical reactions cause formation of a crosslinked polymer composition having a three-dimensional network structure. Commonly used curing agents for fluoroelastomers include difunctional nucleophilic reactants, such as polyhydroxy compounds or diamines. Alternatively, peroxidic curing systems containing organic peroxides and unsaturated coagents, such as polyfunctional isocyanurates, may be employed.
U.S. Pat. No. 4,694,045 discloses several cure site monomers which may be incorporated into E/PAVE/TFE specialty fluoroelastomers. These include brominated or iodinated alpha-olefins, and various halogenated vinyl ethers. Such fluoroelastomers may be cured with peroxides or tin compounds, but not polyhydroxy curatives. However, in many end use applications, it would be beneficial to be able to cure E/PAVE/TFE fluoroelastomers with polyhydroxy compounds because of the improved mold release properties and superior resistance to compression set (i.e. lower compression set) that is imparted by this type of crosslinking system.
Thus, it would be particularly desirable to have an improved specialty E/PAVE/TFE fluoroelastomer that is resistant to alkaline fluids and oil swell and which readily crosslinks with polyhydroxy cure systems to form cured articles having good tensile properties and compression set resistance.